Vibrating meters, such as for example, vibrating densitometers and Coriolis flow meters are generally known and are used to measure mass flow and other information for materials within a conduit. The meter comprises a sensor assembly and an electronics portion. The material within the sensor assembly may be flowing or stationary. Each type of sensor may have unique characteristics, which a meter must account for in order to achieve optimum performance.
Exemplary Coriolis flow meters are disclosed in U.S. Pat. Nos. 4,109,524, 4,491,025, and Re. 31,450 all to J. E. Smith et al. These flow meters have one or more conduits of straight or curved configuration. Each conduit configuration in a Coriolis mass flow meter has a set of natural vibration modes, which may be of simple bending, torsional, or coupled type. Each conduit can be driven to oscillate at a preferred mode.
FIG. 1 shows a prior art sensor assembly 10. The sensor assembly 10 is typically in electrical communication with a meter electronics 20 to form a vibrating meter 5. While the sensor assembly 10 is described below as comprising a portion of a Coriolis flow meter, it should be appreciated that the sensor assembly 10 could just as easily be utilized as another type of vibrating meter. The sensor assembly 10 receives a flowing fluid; however, sensor assemblies of vibrating meters are not necessarily limited to a structure where a fluid under test is flowing. Therefore, the sensor assembly 10 may comprise the vibrating portion of a vibrating densitometer where the fluid is not flowing, the sensing portion of ultra-sonic flow meters, the sensing portion of magnetic volumetric flow meters, etc.
The meter electronics can be connected to the sensor assembly 10 to measure one or more characteristics of a flowing material, such as, for example, density, mass flow rate, volume flow rate, totalized mass flow, temperature, and other information.
The front half of the sensor assembly's case 15 is removed in FIG. 1 to show the interior components. The sensor assembly 10 includes a pair of flanges 101 and 101′, manifolds 102 and 102′, and conduits 103A and 103B. Manifolds 102, 102′ are affixed to opposing ends of the conduits 103A and 103B. The conduits 103A and 103B extend outwardly from the manifolds in an essentially parallel fashion. When the sensor assembly 10 is inserted into a pipeline system (not shown) which carries the flowing material, the material enters sensor assembly 10 through the flange 101, passes through the inlet manifold 102 where the total amount of material is directed to enter conduits 103A, 103B, flows through the conduits 103A, 103B and back into the outlet manifold 102′ where it exits the sensor assembly 10 through the flange 101′.
The sensor assembly 10 can include a driver 104. The driver 104 is shown affixed to conduits 103A, 103B in a position where the driver 104 can vibrate the conduits 103A, 103B in the drive mode, for example. The driver 104 may comprise one of many well-known arrangements such as a coil mounted to the conduit 103A and an opposing magnet mounted on the conduit 103B. A drive signal in the form of an alternating current can be provided by the meter electronics 20, such as for example via first and second wire leads 110, 110′, and passed through the coil to cause both conduits 103A, 103B to oscillate about bending axes W-W and W′-W′. The wire leads 110 and 110′ are coupled to the driver 104 and a first printed circuit board (PCB) 106. Generally the wire leads are coupled to the first PCB 106 and the driver 104 by soldering. A second set of wire leads 120 and 120′ couple the first PCB to a second PCB 107. The second PCB 107 is in electrical communication with the meter electronics via leads 130. The prior art electrical configuration for the driver 104 shown requires four wire leads and two PCBs 106 and 107, resulting in eight soldered joints prior to exiting the sensor assembly's case 15.
The sensor assembly 10 also includes a pair of pick-off sensors 105, 105′ that are affixed to the conduits 103A, 103B. According to an embodiment, the pick-off sensors 105, 105′ may be electromagnetic detectors, for example, pick-off magnets and pick-off coils that produce sensor signals that represent the velocity and position of the conduits 103A, 103B. For example, the pick-off sensors 105, 105′ may supply pick-off signals to the meter electronics 20 via pathways 111, 111′, 112, and 112′, which provide an electrical communication path between the pick-off sensors 105, 105′ and the first PCB 106. A second set of wire leads 121, 121′, 122, and 122′ provide electrical communication between the first and second PCBs 106 and 107 for the pick-off sensors 105, 105′. Therefore, the electrical configuration requires eight wire leads for a total of sixteen solder joints for the pick-off sensors 105, 105′ prior to exiting the sensor assembly's case 15. The power to/from the driver 104 and pick-off sensors 105, 105′ can be regulated using resistors 115, which are shown coupled to the first PCB 106.
Additionally shown are wire leads 113, 113′ for a temperature sensing device such as a resistance temperature detector (RTD) (not shown) that is coupled to the second PCB 107. In some prior art sensor assemblies, the wire leads are also held to the case 15 by tape 114 or some other adhering means to restrict the movement of the leads irrespective of the sensor assembly's orientation.
Those of ordinary skill in the art will appreciate that the motion of the conduits 103A, 103B is proportional to certain characteristics of the flowing material, for example, the mass flow rate and the density of the material flowing through the conduits 103A, 103B.
According to an embodiment, the meter electronics receives the pick-off signals from the pick-off sensors 105, 105′. A path 26 can provide an input and an output means that allows one or more meter electronics 20 to interface with an operator. The meter electronics 20 can measure one or more characteristics of the fluid under test such as, for example, a phase difference, a frequency, a time delay (phase difference divided by frequency), a density, a mass flow rate, a volume flow rate, a totalized mass flow, a temperature, a meter verification, and other information as is generally known in the art.
For example, as material flows into the sensor assembly 10 from a connected pipeline on the inlet side of the sensor assembly 10, it is directed through the conduit 103A, 103B, and exits the sensor assembly 10 through the outlet side of the sensor. The natural vibration modes of the vibrating material filled system are defined in part by the combined mass of the conduits and the material flowing within the conduits.
When there is no flow through the sensor assembly, a driving force applied to the conduits 103A, 103B by the driver 104 causes all points along the conduits 103A, 103B to oscillate with identical phase or small “zero offset,” which is a time delay measured at zero flow. As material begins to flow through the sensor assembly, Coriolis forces cause each point along the conduit(s) to have a different phase. For example, the phase at the inlet end of the sensor lags the phase at the centralized driver position, while the phase at the outlet leads the phase at the centralized driver position. Pick-off sensors 105, 105′ on the conduits 103A, 103B produce sinusoidal signals representative of the motion of the conduits 103A, 103B. Signals output from the pick-off sensors 105, 105′ are processed to determine the phase difference between the pick-off sensors 105, 105′. The phase difference between the two or more pick-off sensors 105, 105′ is proportional to the mass flow rate of the material flowing through the conduits 103A, 103B.
The mass flow rate of the material can be determined by multiplying the phase difference by a Flow Calibration Factor (FCF). Prior to installation of the sensor assembly 10 of the flow meter into a pipeline, the FCF is determined by a calibration process. In the calibration process, a fluid is passed through the flow conduits 103A, 103B at a known flow rate and the relationship between the phase difference and the flow rate is calculated (i.e., the FCF). The sensor assembly 10 of the flow meter 5 subsequently determines a flow rate by multiplying the FCF by the phase difference of the pick-off sensors 105, 105′. In addition, other calibration factors can be taken into account in determining the flow rate.
Due, in part, to the high accuracy of vibrating meters, and Coriolis flow meters in particular, vibrating meters have seen success in a wide variety of industries. However, as mentioned above, the sensor assembly's electrical configuration to communicate with the driver 104 and pick-off sensors 105, 105′ requires an excessive number of wire leads and solder joints. The solder joint typically restricts the temperature range the sensor assembly is capable of handling. Further because each wire lead is typically cut and soldered individually by hand, sensor assemblies are subject to wide variability from one sensor assembly to another. Another problem with the prior art electrical configuration is that the wire leads from the first PCB 106 to the driver 104 and pick-off sensors 105, 105′ are subject to an excessive amount of strain that often leads to premature failure. If a single wire lead breaks, the entire sensor assembly 10 is typically rendered inoperable.
The embodiments described below overcome these and other problems and an advance in the art is achieved. The embodiments described below provide an improved electrical configuration for a sensor assembly that results in a cheaper, more efficient, and more reliable sensor assembly. The improved sensor assembly utilizes a flexible circuit rather than a rigid PCB with various wire leads. Additionally, in some embodiments, the flexible circuit can withstand higher temperatures than the prior art wire leads that are soldered to the sensor components.